1. Field of the Invention
The present invention relates to a device of measuring the concentration of a developer liquid used in a liquid-type printer, which can sense the concentration of a developer liquid by measuring light transmittance.
2. Description of the Related Art
In liquid electrophotographic printers such as liquid-type laser printers, a latent electrostatic image is formed on a photosensitive medium by scanning laser beams thereunto, and then developed by a developer unit using a developer liquid containing toners having a predetermined color. The resultant toner image is transferred on a print paper, resulting in a color image on the print paper. Such liquid electrophotographic printers need a device of measuring the concentration of a developer liquid, to maintain the concentration of the developer liquid supplied to the photosensitive medium within a predetermined range.
Referring to FIG. 1, a conventional device of measuring the concentration of a developer liquid is disposed on a developer liquid supply pathway, which includes a pair of transparent members 1 and 3 along the space of which a developer liquid D flows, and a light emitting device 5 and a light receiving device 7 facing each other while the pair of transparent members 1 and 3 are interposed therebetween. Thus, in measuring the developer liquid, the light receiving device 7 detects the concentration of a developer liquid by receiving light passed through the developer liquid D after being emitted from the light emitting device 5.
In a concentration measuring device having the above configuration, when a developer liquid D is black, which has a relatively low light transmittance compared to other colors, the transparent members 1 and 3 must be spaced by approximately 0.1 mm or less to detect a difference in light transmittance according to the concentration of the developer liquid D. However, as the space between the transparent members 1 and 3 becomes narrow, the flow rate of the developer liquid becomes slow. Accordingly, toner particles stick to the inner walls of the transparent members 1 and 3, thereby lowering light transmittance. Furthermore, it is not possible to remove the toner particles from the inner walls of the transparent members 1 and 3.